Demosaic operation circuit, image sensing device and operation method of the same

ABSTRACT

A demosaic operation circuit includes a white pixel value estimation circuit suitable for acquiring an RGB channel average value and a directional gradient value of a white pixel for each direction using source pixel data provided from a pixel array, and estimating a white pixel value based on the RGB channel average value and the directional gradient value of the white pixel; a fine adjustment circuit suitable for finely adjusting an estimated white pixel value by removing noise through a different filter based on weight values which are differently allocated according to a gradient of a center pixel and a neighboring white pixel; a chroma estimation circuit suitable for estimating a chroma by calculating a chroma array based on the source pixel data and an adjusted white pixel value; and a color correction circuit suitable for correcting a color based on a finely adjusted white pixel value and the chroma.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims priority under 35 U.S.C. § 119 to KoreanPatent Application No. 10-2020-0088976, filed on Jul. 17, 2020, which isherein incorporated by reference in its entirety.

TECHNICAL FIELD

Various embodiments of the present invention generally relate to asemiconductor device. Particularly, various embodiments relate to ademosaic operation circuit, an image sensing device and an operationmethod of the same.

BACKGROUND

Recently, the computer environment paradigm has shifted to ubiquitouscomputing, which enables a computer system to be used virtually anytimeand everywhere. As a result, use of portable electronic devices such asmobile phones, digital cameras, notebook computers and the like has beenrapidly increasing.

Recently, due to the rapid development of display devices, thedevelopment of image photographing devices having image sensors, such ascameras and camcorders, has accelerated. An image photographing devicecan photograph an image and record the photographed image in a recordingmedium, and reproduce the image at any time. Accordingly, since the useof image photographing devices has increased, the demand for morefunctionality in the image photographing device has also increased.Specifically, in addition to compact size, reduced weight, and lowerpower consumption, an image photographing device with higher capabilityfunctionality as well as multi-functions is desirable.

SUMMARY

Embodiments of the present disclosure are directed to a demosaicoperation circuit, an image sensing device and an operation method ofthe same, capable of performing a demosaic operation for an imagepattern having white pixel data of 50% among source pixel data havingRGBW pattern.

In an embodiment, a demosaic operation circuit includes a white pixelvalue estimation circuit suitable for acquiring an RGB channel averagevalue and a directional gradient value of a white pixel for eachdirection using source pixel data provided from a pixel array having aplurality of pixels, and estimating a white pixel value based on the RGBchannel average value and the directional gradient value of the whitepixel for each direction; a fine adjustment circuit suitable for finelyadjusting an estimated white pixel value by removing a noise through adifferent filter based on weight values which are differently allocatedaccording to a gradient of a center pixel and a neighboring white pixel;a chroma estimation circuit suitable for estimating a chroma for eachchannel by calculating a chroma array based on the source pixel data andan adjusted white pixel value; and a color correction circuit suitablefor correcting a color based on a finely adjusted white pixel value andthe chroma for each channel.

The white pixel value estimation circuit may include a white pixel valuecalculation circuit suitable for calculating the directional gradientvalue of the white pixel based on an absolute value of a pixel valuedifference between the white pixels and a pixel value difference betweenpixels having different colors among the source pixel data provided fromthe pixel array; an RGB channel average value calculation circuitsuitable for calculating an RGB channel average value based on alocation of a center pixel among the source pixel data provided from thepixel array; and a white pixel value estimator suitable for estimatingthe white pixel value based on the RGB channel average value and thedirectional gradient value of the white pixel for each direction.

The white pixel value estimation circuit may estimate the white pixelvalue corresponding to the center pixel using a horizontal directionfilter and a vertical direction filter when the center pixel is a greenpixel, a red pixel or a blue pixel.

Fine adjustment circuit may finely adjust the white pixel value based ona gradient value of the estimated white pixel value when the centerpixel is the green pixel, the red pixel or the blue pixel.

The chroma estimation circuit may calculate the chroma array bysubtracting a finely adjusted white pixel value from the source pixeldata.

The chroma estimation circuit may allocate the chroma weight accordingto a chroma similarity for each channel to a chroma value of the centerpixel among the chroma array, and estimates the chroma for each channelbased on an allocated chroma weight.

The chroma estimation circuit may estimate the channel chroma for eachchannel according to the following equation:

${R_{c}^{chroma} = {\sum\limits_{{{({i,j})} \in {kernel}},{R{location}}}^{}{{R^{chroma}\left( {i,j} \right)} \times {R_{wgt}^{chroma}\left( {i,j} \right)}}}}{G_{c}^{chroma} = {\sum\limits_{{{({i,j})} \in {kernel}},{G{location}}}^{}{{G^{chroma}\left( {i,j} \right)} \times {G_{wgt}^{chroma}\left( {i,j} \right)}}}}{B_{c}^{chroma} = {\sum\limits_{{{({i,j})} \in {kernel}},{B{location}}}^{}{{B^{chroma}\left( {i,j} \right)} \times {B_{wgt}^{chroma}\left( {i,j} \right)}}}}$

where R_(c) ^(chroma) represents an estimated chroma of the red pixellocated in the center, G_(c) ^(chroma) represents an estimated chroma ofthe green pixel located in the center, B_(c) ^(chroma) represents anestimated chroma of the blue pixel located in the center, wgt representsa weight, (i,j) represents a location of the red pixel, the green pixeland the blue pixel.

The color correction circuit may correct the color according to thefollowing equation:

$\begin{matrix}{{{fcs}_{gain} = {{DY}_{gain} \times {Edge}_{gain} \times {Color}_{gain}}}{R_{est} = {G_{out} + {{fcs}_{gain} \times \left( {R_{out} - G_{out}} \right)}}}{B_{est} = {B_{out} + {{fcs}_{gain} \times \left( {B_{out} - G_{out}} \right)}}}{R_{out} = {W_{c}^{est} + R_{c}^{chroma}}}{G_{out} = {W_{c}^{est} + G_{c}^{chroma}}}{B_{out} = {W_{c}^{est} + B_{c}^{chroma}}}} & \end{matrix}$

where fcs_(gain) represents an error color correction gain, Dy_(gain)represents a white pixel gain, Edge_(gain) represents an edge gain,Color_(gain) represents a color gain, R_(out) represents a sum of theestimated chroma value and the finely adjusted white pixel value of thered pixel located in the center pixel, G_(out) represents a sum of theestimated chroma value and the finely adjusted white pixel value of thegreen pixel located in the center pixel, B_(out) represents a sum of theestimated chroma value and the finely adjusted white pixel value of theblue pixel located in the center pixel, R_(est) represents a correctedcolor of the red pixel, G_(est) represents a corrected color of thegreen pixel, and B_(est) represents a corrected color of the blue pixel.

In another embodiment, an image sensing device may include an imagesensor including a pixel array having a plurality of pixels; an imagesignal processor suitable for processing an output signal of the imagesensor; and a mosaic operation circuit, wherein the mosaic operationcircuit comprises a white pixel value estimation circuit suitable foracquiring an RGB channel average value and a directional gradient valueof a white pixel for each direction using source pixel data providedfrom a pixel array having a plurality of pixels, and estimating a whitepixel value based on the RGB channel average value and the directionalgradient value of the white pixel for each direction; a fine adjustmentcircuit suitable for finely adjusting an estimated white pixel value byremoving a noise through a different filter based on weight values whichare differently allocated according to a gradient of a center pixel anda neighboring white pixel; a chroma estimation circuit suitable forestimating a chroma for each channel by calculating a chroma array basedon the source pixel data and an adjusted white pixel value; and a colorcorrection circuit suitable for correcting a color based on a fineadjusted white pixel value and the chroma for each channel.

The white pixel value estimation circuit may include a white pixel valuecalculation circuit suitable for calculating the directional gradientvalue of the white pixel based on an absolute value of a pixel valuedifference between the white pixels and a pixel value difference betweenpixels having different colors among the source pixel data provided fromthe pixel array; an RGB channel average value calculation circuitsuitable for calculating an RGB channel average value based on alocation of a center pixel among the source pixel data provided from thepixel array; and a white pixel value estimator ion circuit suitable forestimating the white pixel value based on the RGB channel average valueand the directional gradient value of the white pixel for eachdirection.

The white pixel value estimator estimates the white pixel valuecorresponding to the center pixel using a horizontal direction filterand a vertical direction filter when the center pixel is a green pixel,a red pixel or a blue pixel.

The fine adjustment circuit may finely adjust the white pixel valuebased on a gradient value of the estimated white pixel when the centerpixel is the green pixel, the red pixel or the blue pixel.

The chroma estimation circuit may calculate the chroma array bysubtracting a finely adjusted white pixel value from the source pixeldata.

The chroma estimation circuit may allocate the chroma weight accordingto a chroma similarity for each channel to a chroma value of the centerpixel among the chroma array, and estimates the chroma for each channelbased on an allocated chroma weight.

In another embodiment, an operation method of an image sensing devicemay include acquiring an RGB channel average value and a directionalgradient value of a white pixel for each direction using source pixeldata provided from a pixel array having a plurality of pixels, andestimating a white pixel value based on the RGB channel average valueand the directional gradient value of the white pixel for eachdirection; finely adjusting an estimated white pixel value by removing anoise through a different filter based on weight values which aredifferently allocated according to a gradient of a center pixel and aneighboring white pixel; estimating a chroma for each channel bycalculating a chroma array based on the source pixel data and anadjusted white pixel value; and correcting a color based on a fineadjusted white pixel value and the chroma for each channel.

The estimating of the white pixel value may include calculating thedirectional gradient value of the white pixel based on an absolute valueof a pixel value difference between the white pixels and a pixel valuedifference between pixels having different colors among the source pixeldata provided from the pixel array; calculating an RGB channel averagevalue based on a location of a center pixel among the source pixel dataprovided from the pixel array; and estimating the white pixel valuebased on the RGB channel average value and the directional gradientvalue of the white pixel for each direction.

The estimating of the white pixel value may estimate the white pixelvalue corresponding to the center pixel using a horizontal directionfilter and a vertical direction filter when the center pixel is a greenpixel, a red pixel or a blue pixel.

The finely adjusting of an estimated white pixel value may adjust finelythe white pixel value based on a gradient value of the estimated whitepixel when the center pixel is the green pixel, the red pixel or theblue pixel.

The estimating of a chroma for each channel may calculate the chromaarray by subtracting a finely adjusted white pixel value from the sourcepixel data.

The estimating of a chroma for each channel may allocate the chromaweight according to a chroma similarity for each channel to a chromavalue of the center pixel among the chroma array, and estimates thechroma for each channel based on an allocated chroma weight.

In another embodiment, a non-transitory computer-readable storage mediumstoring executable instructions that, when executed by an image sensingdevice, cause the image sensing device to: acquire an RGB channelaverage value and a directional gradient value of a white pixel for eachdirection using source pixel data provided from a pixel array having aplurality of pixels, and estimating a white pixel value based on the RGBchannel average value and the directional gradient value of the whitepixel for each direction; finely adjust an estimated white pixel valueby removing a noise through a different filter based on weight valueswhich are differently allocated according to a gradient of a centerpixel and a neighboring white pixel; estimate a chroma for each channelby calculating a chroma array based on the source pixel data and anadjusted white pixel value; and correct a color based on a finelyadjusted white pixel value and the chroma for each channel.

These and other features and advantages of the present invention willbecome understood by those with ordinary skill in the art of the presentinvention from the following drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The description herein makes reference to the accompanying drawingswherein like reference numerals refer to like parts throughout theseveral views.

FIG. 1 is a block diagram illustrating a demosaic operation circuit inaccordance with an embodiment of the present disclosure.

FIG. 2 is a diagram illustrating a calculation of white pixel value foreach direction based on a pixel value difference between pixels havingdifferent colors.

FIG. 3 is a diagram illustrating a calculation of white pixel value foreach direction based on a pixel value difference between white pixels.

FIG. 4 is a diagram illustrating an estimated white pixel value of a redpixel disposed in a center.

FIG. 5 is a diagram illustrating a fine adjustment of the white pixelvalue.

FIG. 6 is a diagram illustrating the estimation of a chroma array.

FIG. 7 are graphs illustrating a white pixel gain, an edge gain and acolor gain.

FIG. 8 is a block diagram illustrating an image sensing device employinga demosaic operation circuit in accordance with another embodiment ofthe present disclosure.

FIG. 9 is a block diagram illustrating an image sensing device employinga demosaic operation circuit in accordance with another embodiment ofthe present disclosure.

FIG. 10 is a flow chart illustrating an operation of an image sensingdevice in accordance with another embodiment of the present disclosure.

FIG. 11 is a block diagram illustrating a system configured to implementan image sensing device in accordance with another embodiment of thepresent disclosure.

DETAILED DESCRIPTION

Various examples of the present invention are described below in moredetail with reference to the accompanying drawings. The invention may berealized in other embodiments, forms and variations thereof and shouldnot be construed as being limited to the embodiments set forth herein.Rather, the described embodiments are provided so that this presentdisclosure is thorough and complete and fully conveys the presentinvention to those skilled in the art to which this invention pertains.Throughout the specification, reference to “an embodiment,” “anotherembodiment” or the like does not necessarily mean only one embodiment,and different references to any such phrase are not necessarily to thesame embodiment(s).

It will be understood that, although the terms “first”, “second”,“third”, and so on may be used herein to identify various elements,these elements are not limited by these terms. These terms are used todistinguish one element from another element that otherwise have thesame or similar names. Thus, a first element in one instance may bereferred to as a second or third element in another instance withoutindicating any change in the element itself.

The drawings are not necessarily to scale and, in some instances,proportions may have been exaggerated in order to clearly illustratefeatures of the embodiments. When an element is referred to as beingconnected or coupled to another element, it should be understood thatthe former can be directly connected or coupled to the latter, orelectrically connected or coupled to the latter via one or moreintervening elements. Communication between two elements, whetherdirectly or indirectly connected/coupled, may be wired or wireless,unless the context indicates otherwise. In addition, it will also beunderstood that when an element is referred to as being “between” twoelements, it may be the only element between the two elements, or one ormore intervening elements may also be present.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention.

As used herein, singular forms are intended to include the plural formsand vice versa, unless the context clearly indicates otherwise. Thearticles ‘a’ and ‘an’ as used in this application and the appendedclaims should generally be construed to mean ‘one or more’ unlessspecified otherwise or it is clear from context to be directed to asingular form.

It will be further understood that the terms “comprises,” “comprising,”“includes,” and “including” when used in this specification, specify thepresence of the stated elements and do not preclude the presence oraddition of one or more other elements. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

Unless otherwise defined, all terms including technical and scientificterms used herein have the same meaning as commonly understood by one ofordinary skill in the art to which the present invention pertains. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the present inventionand the relevant art, and not be interpreted in an idealized or overlyformal sense unless expressly so defined herein.

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the invention. Theinvention may be practiced without some or all of these specificdetails. In other instances, well-known process structures and/orprocesses have not been described in detail in order not tounnecessarily obscure the invention.

It is also noted, that in some instances, as would be apparent to thoseskilled in the relevant art, a feature or element described inconnection with one embodiment may be used singly or in combination withother features or elements of another embodiment, unless otherwisespecifically indicated.

Embodiments of the present disclosure are described in detail withreference to the accompanied drawings.

Hereinafter, a demosaic operation circuit is described with reference toFIGS. 1 to 7 .

FIG. 1 is a block diagram illustrating a demosaic operation circuit inaccordance with an embodiment of the present disclosure. FIG. 2 is adiagram illustrating a calculation of white pixel value for eachdirection based on a pixel value difference between pixels havingdifferent colors. FIG. 3 is a diagram illustrating a calculation ofwhite pixel value for each direction based on a pixel value differencebetween white pixels. FIG. 4 is a diagram illustrating an estimatedwhite pixel value of a red pixel disposed in a center. FIG. 5 is adiagram illustrating a fine adjustment of the white pixel value. FIG. 6is a diagram illustrating the estimation of a chroma array. FIG. 7 aregraphs illustrating a white pixel gain, an edge gain and a color gain.

Referring to FIG. 1 , a demosaic operation circuit 300 may include awhite pixel value estimation circuit 310, a fine adjustment circuit 320,a chroma estimation circuit 330 and a color correction circuit 340.

The white pixel value estimation circuit 310 may acquire an RGB channelaverage value and a directional gradient value of a white pixel for eachdirection using source pixel data provided from a pixel array having aplurality of pixels, and estimate a white pixel value based on the RGBchannel average value and the directional gradient value of the whitepixel for each direction.

The white pixel value estimation circuit 310 may include a white pixelvalue calculation circuit 312, an RGB channel average value calculationcircuit 314 and a white pixel value estimator 316.

The white pixel value calculation circuit 312 may calculate adirectional gradient value of the white pixel for each direction basedon an absolute value of a pixel value difference between the whitepixels and a pixel value difference between pixels having differentcolors among the source pixel data provided from the pixel array.

Referring to FIG. 2 , the directional gradient value of the white pixelfor each direction may be calculated using the pixel value differencebetween the pixels having different colors as expressed in equation 1.

$\begin{matrix}{{D_{p33}^{E} = {{❘{\frac{P33}{2} - \frac{P34}{2}}❘} + {❘{\frac{P34}{2} - \frac{P35}{2}}❘} + {❘{\frac{P23}{2} - \frac{P24}{2}}❘} + {❘{\frac{P24}{2} - \frac{P25}{2}}❘} + {❘{\frac{P43}{2} - \frac{P44}{2}}❘} + {❘{\frac{P44}{2} - \frac{P45}{2}}❘}}}{D_{p33}^{H} = {\frac{D_{p33}^{E}}{2} + \frac{D_{p33}^{W}}{2}}}{W_{p33}^{est} = \left\{ {{\begin{matrix}{\frac{{P32} + {P34}}{2},} & {{{where}D_{p33}^{H}} < D_{p33}^{V}} \\{\frac{{P23} + {P43}}{2},} & {{{where}D_{p33}^{V}} < D_{p33}^{H}}\end{matrix}\Delta^{E}} = {\left\{ {{❘\frac{W_{33} - W_{34}}{2}❘} + {❘\frac{W_{23} - W_{24}}{2}❘} + {❘\frac{W_{24} - W_{25}}{2}❘} + {❘\frac{W_{43} - W_{44}}{2}❘} + {❘\frac{W_{44} - W_{45}}{2}❘}} \right\}/4}} \right.}} & \left\lbrack {{Equation}1} \right\rbrack\end{matrix}$

where D_(p33) ^(E) represents a sum of the pixel value differencebetween pixels having different colors along an eastern direction from acenter pixel P33, D_(p33) ^(W) represents a sum of the pixel valuedifference between pixels having different colors along a westerndirection from the center pixel P33, D_(p33) ^(H) represents a sum ofthe pixel value difference between pixels along a horizontal directionfrom the center pixel P33, D_(p33) ^(V) represents a sum of the pixelvalue difference between pixels along a vertical direction from thecenter pixel P33, W_(p33) ^(1st) represents a first estimated whitepixel value, and Δ_(E) represents an gradient value of the white pixelin an eastern direction.

Also, a gradient value of the white pixel in a western direction, agradient value of the white pixel in a southern direction and a gradientvalue of the white pixel in a northern direction may be calculated usingthe same equation as equation 1.

Referring to FIG. 3 , the directional gradient value of the white pixelfor each direction using a pixel value difference between the whitepixels is expressed in equation 2.

$\begin{matrix}{\Delta^{E} = \left\{ \begin{matrix}{{\begin{Bmatrix}{{❘\frac{P_{32} - P_{34}}{2}❘} + {❘\frac{P_{43} - P_{45}}{2}❘} +} \\{{❘\frac{P_{52} - P_{54}}{2}❘} + {❘\frac{P_{63} - P_{65}}{2}❘} +} \\{{❘\frac{P_{23} - P_{25}}{2}❘} + {❘\frac{P_{12} - P_{14}}{2}❘} +} \\{❘\frac{P_{03} - P_{05}}{2}❘}\end{Bmatrix}/8},\begin{matrix}{{where}{cente}\text{r:}} \\{W{location}}\end{matrix}} \\{{\begin{Bmatrix}{{❘\frac{P_{33} - P_{35}}{2}❘} + {❘\frac{P_{42} - P_{44}}{2}❘} +} \\{{❘\frac{P_{53} - P_{55}}{2}❘} + {❘\frac{P_{62} - P_{64}}{2}❘} +} \\{{❘\frac{P_{22} - P_{24}}{2}❘} + {❘\frac{P_{13} - P_{15}}{2}❘} +} \\{❘\frac{P_{02} - P_{04}}{2}❘}\end{Bmatrix}/8},\begin{matrix}{{where}{cente}\text{r:}} \\{R,G,{B{location}}}\end{matrix}}\end{matrix} \right.} & \left\lbrack {{Equation}2} \right\rbrack\end{matrix}$

where, Δ_(E) represents a gradient value of the white pixel in aneastern direction. Also, a gradient value of the white pixel in awestern direction, a gradient value of the white pixel in a southerndirection and a gradient value of the white pixel in a northerndirection may be calculated using the same equation as equation 2.

The RGB channel average value calculation circuit 314 may calculate anRGB channel average value based on a location of a center pixel amongthe source pixel data provided from the pixel array.

The white pixel value estimator 316 may estimate the white pixel valuebased on the RGB channel average value and the directional gradientvalue of the white pixel for each direction.

The estimated white pixel value in the horizontal direction may becalculated as expressed in equation 3.

$\begin{matrix}{{{\overset{\sim}{W}}_{P33} = \frac{{W_{P34}^{W} \times \eta^{W}} + {W_{P32}^{E} \times \eta^{E}}}{\eta^{W} + \eta^{E}}},{\eta^{E} = \frac{1}{\Delta^{E}}},{\eta^{W} = \frac{1}{\Delta^{W}}}} & \left\lbrack {{Equation}3} \right\rbrack\end{matrix}$where Δ_(E) represents a gradient value of the white pixel in an easterndirection, Δ_(W) represents a gradient value of the white pixel in awestern direction, W_(P34) ^(W) represents the white pixel value along awestern direction from a pixel P34, W_(P32) ^(E) represents the whitepixel value along an eastern direction from a pixel P32, and {tilde over(W)}_(P33) represents the estimated white pixel value in a horizontaldirection from the center pixel P33.

The estimated white pixel value in the vertical direction may becalculated as expressed in equation 4.

$\begin{matrix}{{{\overset{\sim}{W}}_{P33} = \frac{{W_{P43}^{S} \times \eta^{S}} + {W_{P23}^{N} \times \eta^{N}}}{\eta^{S} + \eta^{N}}},{\eta^{N} = \frac{1}{\Delta^{N}}},{\eta^{S} = \frac{1}{\Delta^{S}}}} & \left\lbrack {{Equation}4} \right\rbrack\end{matrix}$

where Δ^(N) represents a gradient value of the white pixel in a northerndirection, Δ^(S) represents a gradient value of the white pixel in asouthern direction, W_(P43) ^(S) represents the white pixel value alonga southern direction from a pixel P43, W_(P23) ^(N) represents the whitepixel value along a northern direction from a pixel P23, and {tilde over(W)}_(P33) represents the estimated white pixel value in a verticaldirection from the center pixel P33.

Also, the estimated white pixel value in the horizontal/verticaldirection may be calculated as expressed in equation 5.

$\begin{matrix}{{{\overset{\sim}{W}}_{P33} = \frac{{W_{P34}^{E} \times \eta^{E}} + {W_{P32}^{W} \times \eta^{W}} + {W_{P43}^{S} \times \eta^{S}} + {W_{P23}^{N} \times \eta^{N}}}{\eta^{E} + \eta^{W} + \eta^{S} + \eta^{N}}},{\eta^{E} = \frac{1}{\Delta^{E}}},{\eta^{W} = \frac{1}{\Delta^{W}}},{\eta^{N} = \frac{1}{\Delta^{N}}},{\eta^{S} = \frac{1}{\Delta^{S}}}} & \left\lbrack {{Equation}5} \right\rbrack\end{matrix}$

where W_(P34) ^(W) represents the white pixel value along a westerndirection from a pixel P34, W_(P32) ^(E) represents the white pixelvalue along an eastern direction from a pixel P32, W_(P43) ^(S)represents the white pixel value along a southern direction from a pixelP43, W_(P23) ^(N) represents the white pixel value along a northerndirection from a pixel P23, Δ_(E) represents a gradient value of thewhite pixel in an eastern direction, Δ^(W) represents a gradient valueof the white pixel in a western direction, Δ^(N) represents a gradientvalue of the white pixel in a northern direction, Δ^(S) represents agradient value of the white pixel in a southern direction, and {tildeover (W)}_(P33) represents the estimated white pixel value in ahorizontal/vertical direction from the center pixel P33.

The fine adjustment circuit 320 may finely adjust an estimated whitepixel value by removing a noise from the estimated white pixel valuethrough a different filter based on weight values which are differentlyallocated according to a gradient of a center pixel and a neighboringwhite pixel.

For example, referring to FIG. 4 , the estimated white pixel value Wc ofthe red pixel R33 located in a center of a 7×7 pixel array may be finelyadjusted.

Also, when the center pixel P33 is a blue pixel or a green pixel, theestimated white pixel value may be finely adjusted by removing the noiseusing the estimated white pixel value through a horizontal filter, avertical filter or a horizontal/vertical filter.

Referring to FIG. 5 , if a value obtained by multiplying a predeterminedweight (α) and the sum of the gradient value of the white pixel in theeastern direction and the gradient value of the white pixel in thewestern direction is less than the sum of the gradient value of thewhite pixel in the southern direction and the gradient value of thewhite pixel in the northern direction, the estimated white pixel valuemay be finely adjusted by removing the noise through the horizontalfilter.

Also, if the value obtained by multiplying a predetermined weight (α)and the sum of the gradient value of the white pixel in the easterndirection and the gradient value of the white pixel in the westerndirection is greater than the sum of the gradient value of the whitepixel in the southern direction and the gradient value of the whitepixel in the northern direction, the estimated white pixel value may befinely adjusted by removing the noise through the vertical filter.

Also, if the value obtained by multiplying a predetermined weight (α)and the sum of the gradient value of the white pixel in the easterndirection and the gradient value of the white pixel in the westerndirection is same as the sum of the gradient value of the white pixel inthe southern direction and the gradient value of the white pixel in thenorthern direction, the estimated white pixel value may be finelyadjusted by removing the noise through the horizontal/vertical filter.

The chroma estimation circuit 330 may estimate a chroma for each channelby calculating a chroma array based on the source pixel data and anadjusted white pixel value.

More specifically, referring to FIG. 6 , the chroma estimation circuit330 may calculate the chroma array by subtracting the adjusted whitepixel value from the source pixel data of a Bayer pattern. The chromaestimation circuit 330 may allocate the chroma weight according to achroma similarity for each channel to a chroma value of the center pixelamong the chroma array, and estimate the chroma for each channel basedon the allocated chroma weight.

The chroma for each channel may be estimated as expressed in equation 6.

$\begin{matrix}{{R_{c}^{chroma} = {\sum\limits_{{{({i,j})} \in {kernel}},{R{location}}}^{}{{R^{chroma}\left( {i,j} \right)} \times {R_{wgt}^{chroma}\left( {i,j} \right)}}}}{G_{c}^{chroma} = {\sum\limits_{{{({i,j})} \in {kernel}},{G{location}}}^{}{{G^{chroma}\left( {i,j} \right)} \times {G_{wgt}^{chroma}\left( {i,j} \right)}}}}{B_{c}^{chroma} = {\sum\limits_{{{({i,j})} \in {kernel}},{B{location}}}^{}{{B^{chroma}\left( {i,j} \right)} \times {B_{wgt}^{chroma}\left( {i,j} \right)}}}}} & \left\lbrack {{Equation}6} \right\rbrack\end{matrix}$

where R_(c) ^(chroma) represents an estimated chroma of the red pixellocated in the center pixel, G_(c) ^(chroma) represents an estimatedchroma of the green pixel located in the center pixel, B_(c) ^(chroma)represents an estimated chroma of the blue pixel located in the centerpixel, wgt represents a weight value, (i,j) represents a location of thered pixel, the green pixel and the blue pixel.

The color correction circuit 340 may correct the color based on a finelyadjusted white pixel value of the fine adjustment circuit 320 and theestimated chroma of the red pixel, the green pixel and the blue pixel ofthe chroma estimation circuit 330.

Referring to FIG. 7 , the color correction may be optimized using thewhite pixel gain DY_(gain), the edge gain Edge_(gain) and the color gainColor_(gain). That is, the color correction may be calculated asexpressed in equation 7.

$\begin{matrix}{{{fcs}_{gain} = {{DY}_{gain} \times {Edge}_{gain} \times {Color}_{gain}}}{R_{est} = {G_{out} + {{fcs}_{gain} \times \left( {R_{out} - G_{out}} \right)}}}{B_{est} = {B_{out} + {{fcs}_{gain} \times \left( {B_{out} - G_{out}} \right)}}}{R_{out} = {W_{c}^{est} + R_{c}^{chroma}}}{G_{out} = {W_{c}^{est} + G_{c}^{chroma}}}{B_{out} = {W_{c}^{est} + B_{c}^{chroma}}}} & \left\lbrack {{Equation}7} \right\rbrack\end{matrix}$

where fcs_(gain) represents an error color correction gain, Dy_(gain)represents a white pixel gain, Color_(gain) represents a color gain,R_(out) represents the sum of the estimated chroma value and the finelyadjusted white pixel value of the red pixel located in the center,G_(out) represents the sum of the estimated chroma value and the finelyadjusted white pixel value of the green pixel located in the center,B_(out) represents the sum of the estimated chroma value and the finelyadjusted white pixel value of the blue pixel located in the center,R_(est) represents a corrected color of the red pixel, G_(est)represents a corrected color of the green pixel, and B_(est) representsa corrected color of the blue pixel.

FIG. 8 is a block diagram illustrating an image sensing device 10 inaccordance with an embodiment of the present disclosure.

Referring to FIG. 8 , the image sensing device 10 may include an imagesensor 100 and an image signal processor (ISP) 400.

The image sensing device 10 may be implemented in any suitableelectronic device, such as a personal computer (PC) or a mobilecomputing device that can receive and process image data.

More specifically, the image sensing device 10 may be implemented in alaptop computer, a mobile phone, a smart phone, a tablet, a personaldigital assistant (PDA), an enterprise digital assistant (EDA), adigital still camera, a digital video camera, a portable multimediaplayer (PMP), a mobile internet device (MID), a wearable computer, as anobject in an Internet of things (IoT) network, or as an object in aninternet of everything (IoE) network.

The image sensor 100 may include a pixel array 200 and a demosaicoperation circuit 300.

The pixel array 200 may include a plurality of pixels. Herein, eachpixel may represent pixel data, and have an RGB data format, YUV dataformat, YCbCr data format, or any other data format consistent with theteachings herein.

The demosaic operation circuit 300 may perform a demosaic operation ofRGBW pattern having a white pixel of 50%.

The demosaic operation circuit 300 may be implemented as shown in FIGS.1 to 7 .

The detailed configuration and operations of the demosaic operationcircuit 300 are described in detail with reference to FIGS. 1 to 7 .

The image signal processor 400 may be implemented in an integratedcircuit, a system on chip (SoC) or a mobile application processor. Theimage signal processor 400 may process an output signal of the imagesensor 100. That is, the image signal processor 400 may receive andprocess an image output signal outputted from the demosaic operationcircuit 300 of the image sensor 100.

More specifically, the image signal processor 400 may generate RGB imagedata from a Bayer pattern corresponding to pixel data. For example, theimage signal processor 400 may process a Bayer pattern such that theimage data is displayed in a display, and may transfer processed imagedata to an interface for transfer to another component or device.

In an embodiment, each of the image sensor 100 and the image signalprocessor 400 may be implemented as a multi-chip package (MCP). Inanother embodiment, the image sensor 100 and the image signal processor400 may be implemented as a single chip.

FIG. 9 is a block diagram illustrating an image sensing device 10 inaccordance with an embodiment of the present disclosure.

Referring to FIG. 9 , the image sensing device 10 may include an imagesensor 100 and an image signal processor (ISP) 400. The image signalprocessor 400 may include a demosaic operation circuit 300.

The demosaic operation circuit 300 may be implemented as shown in FIGS.1 to 7 .

The structure and operation of the image sensing device 10 shown in FIG.9 are substantially the same as the structure and operation of the imagesensing device 10 shown in FIG. 8 , except that the demosaic operationcircuit 300 is implemented in the image signal processor 400 instead ofin the image sensor 100. Thus, a detailed description of the imagesensing device 10 of FIG. 9 is omitted.

Hereinafter, an operation of an image sensing device in accordance withan embodiment of the present disclosure is described with reference toFIG. 10 . FIG. 10 is a flow chart illustrating an operation of an imagesensing device (e.g., image sensing device 10 in FIGS. 8 and 9 ) inaccordance with an embodiment of the present disclosure.

Referring to FIG. 10 , the operation of an image sensing device mayinclude an estimation of a white pixel value S1000, a fine adjustment ofestimated white pixel value S1100, a chroma estimation for each channelS1200 and a color correction S1300.

At operation S1000, an RGB channel average value and a directionalgradient value of a white pixel for each direction may be acquired usingsource pixel data provided from a pixel array having a plurality ofpixels. The white pixel value may be estimated based on the RGB channelaverage value and the directional gradient value of the white pixel foreach direction.

More specifically, the estimation of the white pixel value S1000 mayinclude a calculation operation of the gradient value of the white pixelfor each direction S1010, a calculation operation of an RGB channelaverage value S1020 and an estimation operation of the white pixel valueS1030.

At operation S1010, the directional gradient of the white pixel for eachdirection may be calculated based on an absolute value of a pixel valuedifference between the white pixels and a pixel value difference betweenpixels having different colors among the source pixel data provided fromthe pixel array.

At operation S1020, the calculation of the RGB channel average value maybe calculated according to a location of a center pixel among the sourcepixel data provided from the pixel array.

At operation S1030, the white pixel value may be estimated based on theRGB channel average value and the directional gradient value of thewhite pixel for each direction.

Herein, when the center pixel is a green pixel, a red pixel or a bluepixel, the white pixel value corresponding to the center pixel may beestimated using the horizontal direction filter and the verticaldirection filter.

At operation S1100, the estimated white pixel value may be finelyadjusted by removing a noise from the estimated white pixel valuethrough a different filter based on weight values which are differentlyallocated according to a gradient of a center pixel and a neighboringwhite pixel.

At operation S1200, the chroma for each channel may be estimated bycalculating a chroma array based on the source pixel data and the finelyadjusted white pixel value.

Herein, the chroma array may be calculated by subtracting a finelyadjusted white pixel value from the source pixel data.

Also, the chroma weight may be allocated according to a chromasimilarity for each channel to the chroma value of the center pixelamong the chroma array, and the chroma for each channel may be estimatedaccording to the allocated chroma weight.

Hereinafter, a system configured to implement an image sensing device inaccordance with an embodiment of the present disclosure is described indetail with reference to FIG. 11 .

FIG. 11 illustrates a system configured to implement an image sensingdevice in accordance with an embodiment of the present disclosure.

In various embodiments, the system of FIG. 11 may be any of varioustypes of computing devices, including, but not limited to, a personalcomputer system, desktop computer, laptop or notebook computer,mainframe computer system, handheld computing device, cellular phone,smartphone, mobile phone, workstation, network computer, a consumerdevice, application server, storage device, intelligent display, aperipheral device such as a switch, modem, router, etc., or in generalany type of computing device. According to an embodiment, the system ofFIG. 11 may represent a system-on-a-chip (SoC). The circuits of the SoC1000 may be integrated onto a single semiconductor substrate as anintegrated circuit, i.e., a “chip.” In some embodiments, the circuitsmay be implemented on two or more discrete chips in a system. The SoC1000 will be used as an example herein.

In the illustrated embodiment, the circuits of the SoC 1000 include acentral processing unit (CPU) complex 1020, on-chip peripheral circuits1040A-1040B (individually, “peripheral” and collectively “peripherals”),a memory controller (MC) 1030, a communication fabric 1010, and an imagesignal processor 400. The SoC 1000 may also be coupled to additionalcircuits, such as to a memory 1800 and an image sensor 100. The circuits1020, 1030, 1040A-1040B, and 400 may all be coupled to the communicationfabric 1010. The memory controller 1030 may be coupled to the memory1800, and the peripheral 1040B may be coupled to an outer interface1900. Additionally, the image signal processor 400 may be coupled to theimage sensor 100.

The peripherals 1040A-1040B may be any set of additional hardwarefunctionality in the SoC 1000. For example, the peripherals 1040A-1040Bmay include display controllers configured to display video data on oneor more display devices, graphics processing units (GPUs), videoencoder/decoders, scalers, rotators, blenders, etc.

The image signal processor 400 may, in some embodiments, be part ofanother video peripheral configured to process image capture data fromthe image sensor 100 (or other image sensor). The image signal processor400 and the image sensor 100 may be configured to implement the imagesignal processor 400 and the image sensor 100 shown in FIGS. 1 to 10 .

The peripherals 1040A-1040B may also include audio peripherals such asmicrophones, speakers, interfaces to microphones and speakers, audioprocessors, digital signal processors, mixers, etc. The peripherals1040A-1040B (e.g., the peripheral 1040B) may include peripheralinterface controllers for various interfaces 1900 external to the SoC1000 including interfaces such as Universal Serial Bus (USB), peripheralcircuit interconnect (PCI) including PCI Express (PCIe), serial andparallel ports, etc. The peripherals 1040A-1040B may further includenetworking peripherals such as media access controllers (MACs). Ingeneral, any set of hardware may be included, according to variousembodiments.

The CPU complex 1020 may include one or more processors (Ps) 1024 thatserve as the CPU of the SoC 1000. The processor(s) 1024 may execute themain control software of the system, such as an operating system.Generally, software executed by the CPU may control the other circuitsof the system to realize the desired functionality of the system. Theprocessors 1024 may also execute other software, such as applicationprograms. The application programs may provide user functionality andmay rely on the operating system for lower level device control.Accordingly, the processors 1024 may also be referred to as applicationprocessors. The CPU complex 1020 may further include other hardware suchas the L2 cache 1022 and/or an interface to the other circuits of thesystem (e.g., an interface to the communication fabric 1010).

Generally, a processor may include any circuitry and/or microcodeconfigured to execute instructions defined in an instruction setarchitecture implemented by the processor. The instructions and dataoperated on by the processors in response to executing the instructionsmay generally be stored in the memory 1800, although certaininstructions may be defined for direct processor access to peripheralsas well. Processors may encompass processor cores implemented on anintegrated circuit with other circuits as a system on a chip (SoC 1000)or other levels of integration. Processors may further encompassdiscrete microprocessors, processor cores and/or microprocessorsintegrated into multichip module implementations, processors implementedas multiple integrated circuits, etc.

The memory controller 1030 may generally include circuitry for receivingmemory operations from other circuits of the SoC 1000 and for accessingthe memory 1800 to complete the memory operations. The memory controller1030 may be configured to access any type of memory 1800. For example,the memory 1800 may be a static random access memory (SRAM), or adynamic RAM (DRAM) such as synchronous DRAM (SDRAM) including doubledata rate (DDR, DDR2, DDR3, etc.) DRAM. Low power/mobile versions of theDDR DRAM may be supported (e.g. LPDDR, mDDR, etc.). The memorycontroller 1030 may include queues for memory operations, for ordering(and potentially reordering) the operations and presenting theoperations to the memory 1800. The memory controller 1030 may furtherinclude data buffers to store write data awaiting write to memory andread data awaiting return to the source of the memory operation. In someembodiments, the memory controller 1030 may include a memory cache tostore recently accessed memory data. In SoC implementations, forexample, the memory cache may reduce power consumption in the SoC byavoiding re-access of data from the memory 1800 if it is expected to beaccessed again soon. In some cases, the memory cache may also bereferred to as a system cache, as opposed to private caches such as theL2 cache 1022 or caches in the processors 1024, which serve only certaincircuits. Additionally, in some embodiments, a system cache may belocated externally to the memory controller 1030.

In an embodiment, the memory 1800 may be packaged with the SoC 1000 in achip-on-chip or package-on-package configuration. A multichip moduleconfiguration of the SoC 1000 and the memory 1800 may be used as well.Such configurations may be relatively more secure (in terms of dataobservability) than transmissions to other circuits in the system (e.g.to the end points). Accordingly, protected data may reside in the memory1800 unencrypted, whereas the protected data may be encrypted forexchange between the SoC 1000 and external endpoints.

The communication fabric 1010 may be any communication interconnect andprotocol for communicating among the circuits of the SoC 1000. Thecommunication fabric 1010 may be bus-based, including shared busconfigurations, cross bar configurations, and hierarchical buses withbridges. The communication fabric 1010 may also be packet-based, and maybe hierarchical with bridges, cross bar, point-to-point, or otherinterconnects.

It is noted that the number of circuits of the SoC 1000 (and the numberof subcircuits within the CPU complex 1020) may vary in differentembodiments. There may be more or fewer of each circuit/subcircuit thanthe number shown in FIG. 11 .

In some embodiments, the methods described herein may be implemented bya computer program product, or software. In some embodiments, anon-transitory, computer-readable storage medium may have stored thereoninstructions which may be used to program a computer system (or otherelectronic devices) to perform some or all of the techniques describedherein. A computer-readable storage medium may include any mechanism forstoring information in a form (e.g., software, processing application)readable by a machine (e.g., a computer). The machine-readable mediummay include, but is not limited to, magnetic storage medium (e.g.,floppy diskette); optical storage medium (e.g., CD-ROM); magneto-opticalstorage medium; read only memory (ROM); random access memory (RAM);erasable programmable memory (e.g., EPROM and EEPROM); flash memory;electrical, or other types of medium suitable for storing programinstructions. In addition, program instructions may be communicatedusing optical, acoustical or other forms of propagated signal (e.g.,carrier waves, infrared signals, digital signals, etc.).

As described above, a demosaic operation circuit, an image sensingdevice and an operation method of the same in accordance withembodiments of the present disclosure may perform a demosaic operationfor an image pattern having white pixel data of 50% among source pixeldata having RGBW pattern.

While the present disclosure illustrates and describes specificembodiments, it will be apparent to those skilled in the art in light ofthe present disclosure that various changes and modifications may bemade without departing from the spirit and scope of the invention asdefined in the following claims. The present invention encompasses allsuch changes and modifications to the extent the changes andmodifications fall within the scope of the claims.

What is claimed is:
 1. A demosaic operation circuit, comprising: a whitepixel value estimation circuit suitable for acquiring an RGB channelaverage value and a directional gradient value of a white pixel for eachdirection using source pixel data provided from a pixel array having aplurality of pixels, and estimating a white pixel value based on the RGBchannel average value and the directional gradient value of the whitepixel for each direction; a fine adjustment circuit suitable for finelyadjusting an estimated white pixel value by removing a noise through adifferent filter based on weight values which are differently allocatedaccording to a gradient of a center pixel and a neighboring white pixel;a chroma estimation circuit suitable for estimating a chroma for eachchannel by calculating a chroma array based on the source pixel data anda finely adjusted white pixel value; and a color correction circuitsuitable for correcting a color based on the finely adjusted white pixelvalue and the chroma for each channel.
 2. The demosaic operation circuitof claim 1, wherein the white pixel value estimation circuit includes: awhite pixel value calculation circuit suitable for calculating thedirectional gradient value of the white pixel based on an absolute valueof a pixel value difference between the white pixels and a pixel valuedifference between pixels having different colors among the source pixeldata provided from the pixel array; an RGB channel average valuecalculation circuit suitable for calculating an RGB channel averagevalue based on a location of a center pixel among the source pixel dataprovided from the pixel array; and a white pixel value estimatorsuitable for estimating the white pixel value based on the RGB channelaverage value and the directional gradient value of the white pixel foreach direction.
 3. The demosaic operation circuit of claim 2, whereinthe white pixel value estimator estimates the white pixel valuecorresponding to the center pixel using a horizontal direction filterand a vertical direction filter when the center pixel is a green pixel,a red pixel or a blue pixel.
 4. The demosaic operation circuit of claim3, wherein the fine adjustment circuit finely adjusts the white pixelvalue based on a gradient value of the estimated white pixel value whenthe center pixel is the green pixel, the red pixel or the blue pixel. 5.The demosaic operation circuit of claim 1, wherein the chroma estimationcircuit calculates the chroma array by subtracting the finely adjustedwhite pixel value from the source pixel data.
 6. The demosaic operationcircuit of claim 5, wherein the chroma estimation circuit allocateschroma weight according to a chroma similarity for each channel to achroma value of the center pixel among the chroma array, and estimatesthe chroma for each channel based on an allocated chroma weight.
 7. Thedemosaic operation circuit of claim 6, wherein the chroma estimationcircuit estimates the chroma for each channel according to the followingequation:${R_{c}^{chroma} = {\sum\limits_{{{({i,j})} \in {kernel}},{R{location}}}^{}{{R^{chroma}\left( {i,j} \right)} \times {R_{wgt}^{chroma}\left( {i,j} \right)}}}}{G_{c}^{chroma} = {\sum\limits_{{{({i,j})} \in {kernel}},{G{location}}}^{}{{G^{chroma}\left( {i,j} \right)} \times {G_{wgt}^{chroma}\left( {i,j} \right)}}}}{B_{c}^{chroma} = {\sum\limits_{{{({i,j})} \in {kernel}},{B{location}}}^{}{{B^{chroma}\left( {i,j} \right)} \times {B_{wgt}^{chroma}\left( {i,j} \right)}}}}$where R_(c) ^(chroma) represents an estimated chroma of the red pixellocated in the center, G_(c) ^(chroma) represents an estimated chroma ofthe green pixel located in the center, B_(c) ^(chroma) represents anestimated chroma of the blue pixel located in the center, wgt representsa weight, (i,j) represents a location of the red pixel, the green pixeland the blue pixel.
 8. The demosaic operation circuit of claim 7,wherein the color correction circuit corrects the color according to thefollowing equation:fcs _(gain) =DY _(gain)×Edge_(gain)×Color_(gain)R _(est) =G _(out) +fcs _(gain)×(R _(out) −G _(out))B _(est) =B _(out) +fcs _(gain)×(B _(out) −G _(out))R _(out) =W _(c) ^(est) +R _(c) ^(chroma)G _(out) =W _(c) ^(est) +G _(c) ^(chroma)B _(out) =W _(c) ^(est) +B _(c) ^(chroma) where fcs_(gain) represents anerror color correction gain, DY_(gain) represents a white pixel gain,Edge_(gain) represents an edge gain, Color_(gain) represents a colorgain, R_(out) represents a sum of the estimated chroma value and thefinely adjusted white pixel value of the red pixel located in the centerpixel, G_(out) represents a sum of the estimated chroma value and thefinely adjusted white pixel value of the green pixel located in thecenter pixel, B_(out) represents a sum of the estimated chroma value andthe finely adjusted white pixel value of the blue pixel located in thecenter pixel, R_(est) represents a corrected color of the red pixel,G_(est) represents a corrected color of the green pixel, and B_(est)represents a corrected color of the blue pixel.
 9. An image sensingdevice, comprising: an image sensor including a pixel array having aplurality of pixels; an image signal processor suitable for processingan output signal of the image sensor; and a mosaic operation circuit,wherein the mosaic operation circuit comprises a white pixel valueestimation circuit suitable for acquiring an RGB channel average valueand a directional gradient value of a white pixel for each directionusing source pixel data provided from a pixel array having a pluralityof pixels, and estimating a white pixel value based on the RGB channelaverage value and the directional gradient value of the white pixel foreach direction; a fine adjustment circuit suitable for finely adjustingan estimated white pixel value by removing a noise through a differentfilter based on weight values which are differently allocated accordingto a gradient of a center pixel and a neighboring white pixel; a chromaestimation circuit suitable for estimating a chroma for each channel bycalculating a chroma array based on the source pixel data and a finelyadjusted white pixel value; and a color correction circuit suitable forcorrecting a color based on the finely adjusted white pixel value andthe chroma for each channel.
 10. The image sensing device of claim 9,wherein the white pixel value estimation circuit includes: a white pixelvalue calculation circuit suitable for calculating the directionalgradient value of the white pixel based on an absolute value of a pixelvalue difference between the white pixels and a pixel value differencebetween pixels having different colors among the source pixel dataprovided from the pixel array; an RGB channel average value calculationcircuit suitable for calculating an RGB channel average value based on alocation of a center pixel among the source pixel data provided from thepixel array; and a white pixel value estimator suitable for estimatingthe white pixel value based on the RGB channel average value and thedirectional gradient value of the white pixel for each direction. 11.The image sensing device of claim 10, wherein the white pixel valueestimator estimates the white pixel value corresponding to the centerpixel using a horizontal direction filter and a vertical directionfilter when the center pixel is a green pixel, a red pixel or a bluepixel.
 12. The image sensing device of claim 11, wherein the fineadjustment circuit finely adjusts the white pixel value based on agradient value of the estimated white pixel value when the center pixelis the green pixel, the red pixel or the blue pixel.
 13. The imagesensing device of claim 9, wherein the chroma estimation circuitcalculates the chroma array by subtracting the finely adjusted whitepixel value from the source pixel data.
 14. The image sensing device ofclaim 13, wherein the chroma estimation circuit allocates chroma weightaccording to a chroma similarity for each channel to a chroma value ofthe center pixel among the chroma array, and estimates the chroma foreach channel based on an allocated chroma weight.
 15. An operationmethod of an image sensing device, comprising: acquiring an RGB channelaverage value and a directional gradient value of a white pixel for eachdirection using source pixel data provided from a pixel array having aplurality of pixels, and estimating a white pixel value based on the RGBchannel average value and the directional gradient value of the whitepixel for each direction; finely adjusting an estimated white pixelvalue by removing a noise through a different filter based on weightvalues which are differently allocated according to a gradient of acenter pixel and a neighboring white pixel; estimating a chroma for eachchannel by calculating a chroma array based on the source pixel data anda finely adjusted white pixel value; and correcting a color based on thefinely adjusted white pixel value and the chroma for each channel. 16.The operation method of claim 15, wherein the estimating of the whitepixel value includes: calculating the directional gradient value of thewhite pixel based on an absolute value of a pixel value differencebetween the white pixels and a pixel value difference between pixelshaving different colors among the source pixel data provided from thepixel array; calculating an RGB channel average value based on alocation of a center pixel among the source pixel data provided from thepixel array; and estimating the white pixel value based on the RGBchannel average value and the directional gradient value of the whitepixel for each direction.
 17. The operation method of claim 16, whereinthe estimating of the white pixel value estimates the white pixel valuecorresponding to the center pixel using a horizontal direction filterand a vertical direction filter when the center pixel is a green pixel,a red pixel or a blue pixel.
 18. The operation method of claim 17,wherein the finely adjusting of an estimated white pixel value adjustsfinely the white pixel value based on a gradient value of the estimatedwhite pixel value when the center pixel is the green pixel, the redpixel or the blue pixel.
 19. The operation method of claim 18, whereinthe estimating of a chroma for each channel calculates the chroma arrayby subtracting the finely adjusted white pixel value from the sourcepixel data.
 20. The operation method of claim 19, wherein the estimatingof a chroma for each channel allocates chroma weight according to achroma similarity for each channel to a chroma value of the center pixelamong the chroma array, and estimates the chroma for each channel basedon an allocated chroma weight.